This application claims the benefit of a Japanese Patent Application No.2002-229393 filed Aug. 7, 2002, in the Japanese Patent Office, the disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to timing recovery methods and storage apparatuses, and more particularly to a timing recovery method which is used when reproducing information from a recording medium such as a magnetic disk, an optical disk and a magneto-optical disk, and to a storage apparatus which employs such a timing recovery method.
2. Description of the Related Art
FIG. 1 is a system block diagram showing a structure of an important part of a magnetic storage apparatus which employs an example of a conventional timing recovery method, that is, a structure of a timing recovery section. The magnetic storage apparatus shown in FIG. 1 includes a gain controller 1, a voltage gain amplifier (VGA) 2, a continuous transfer function (CTF) analog filter 3, an analog-to-digital converter (ADC) 4, a finite impulse response (FIR) filter 5, a detector 6, an RLL decoder 7, a phase comparator 8, a loop filter 9, and a voltage controlled oscillator (VCO) 10.
A reproduced signal is output from a head 11 which reads a magnetic recording medium 12 such as a magnetic disk. This reproduced signal is passes through the VGA 2, which has a gain controlled by the gain controller 1, and the CTF analog filter 3, and is sampled by the ADC 4. Data of the sampled signal are equalized by the FIR filter 5, and compared in the phase comparator 8 with samples detected by the detector 6. A phase error signal is calculated by and output from the phase comparator 8. The phase error signal passes through the loop filter 9, and controls an oscillation frequency of the VCO 10. Hence, a feedback loop is formed in which the sampling positions of the ADC 4 are controlled. An output of the detector 6 is decoded by the RLL decoder 7 and supplied to a controller (not shown) within the magnetic storage apparatus.
Conventionally, the signal detected by the detector 6 is used as a target value when calculating the phase error signal in the phase comparator 8. For this reason, when an error exists in the output signal of the detector 6, an erroneous target value is used in the phase comparator 8, thereby causing the timing recovery section to respond to an erroneous phase error signal.
In a case where a signal-to-noise ratio (SNR) is good, the possibility that an error exists in the output signal of the detector 6 is low. But under low SNR conditions, the possibility that the error exists in the output signal of the detector 6 is high, thereby causing the timing recovery section to respond to the erroneous phase error signal and causing a problem in that a stable timing recovery cannot be carried out.